not true. unity works well, its cross-platform and well known.
surely the importance is that u know how to code and u are satisfied with the result.
I mean, what is the best engine? rpgmaker? ren'py? unreal? c++? html5?
theres a lot of different one to pick but in the end will it really matter?
maybe its not crossplatform. that will limit who can play it. otherwise I dont see any problems at all.
Unity is better, IMO, for a 3D game. It limits implementation of mods (gallery, walkthroughs in-game, ports to Android, etc) and even modders who knows how to work with Unity. But it usually falls to the programmer. The Secret of Hokwiton, for example, it has like 1 save slot, but My Wife's a Star has several, even though it's a limit amount.
I'm not saying Unity is a bad engine, it's a powerful engine, but specifically for AVN, IMO again, it's just not the best.
But I certainly wish for his game to be successful. All the good luck to him